Department of Biology, University of Maryland College Park, College Park, MD 20742, USA.
Mol Ecol. 2011 Jan;20(2):299-310. doi: 10.1111/j.1365-294X.2010.04935.x. Epub 2010 Nov 19.
The expression of cone opsin genes is a primary determinant of the characteristics of colour vision. Interspecific variation in opsin expression is common in African cichlids. It is correlated with foraging among cichlids from Lake Malawi, and with ambient light environment among cichlids from Lake Victoria. In this study, we tested whether gene expression varied within species such that it might be important in contributing to divergence. We hypothesized that light attenuation with depth would be correlated with predictable changes in gene expression in Lake Malawi, and that this variation would tune visual sensitivities to match the ambient light environment. We observed significant differences in cone opsin expression in three different comparisons among populations of the same species. Higher LWS expression was found in shallow versus deep Copadichromis eucinostomus. In Metriaclima zebra, individuals from Zimbawe Rock expressed significantly more SWS2B than those from Thumbi West Island, although these locales have similar ambient light environments. Finally, Tropheops gracilior from deeper water had significantly more variation in expression than their shallow counterparts. These results support that gene expression varies significantly between populations of the same species. Surprisingly, these results could not be explained by predicted visual performance as models predicted that differential expression patterns did not confer sensitivity advantages at different depths. This suggested that expression variation did not confer a local sensitivity advantage. Therefore, our findings were contrary to a primary requirement of the sensory bias hypothesis. As such, other explanations for intraspecific gene expression variation need to be tested.
视蛋白基因的表达是颜色视觉特征的主要决定因素。在非洲丽鱼科鱼类中，视蛋白表达的种间变异很常见。这种变异与马拉维湖丽鱼的觅食行为有关，也与维多利亚湖丽鱼的环境光照有关。在这项研究中，我们测试了物种内的基因表达是否存在差异，因为这种差异可能对物种的分化很重要。我们假设，随着深度的增加，光衰减会与马拉维湖中可预测的基因表达变化相关，这种变化会使视觉敏感性适应环境光照。我们观察到同一种群的三个不同种群之间的视蛋白表达存在显著差异。在浅水区 Copadichromis eucinostomus 中，LWS 的表达高于深水区。在 Metriaclima zebra 中，津巴布韦岩的个体比 Thumbi West Island 的个体表达出更多的 SWS2B，尽管这两个地方的环境光照相似。最后，来自深水区的 Tropheops gracilior 的表达变化比来自浅水区的个体更为显著。这些结果表明，在同一物种的不同种群之间，基因表达存在显著差异。令人惊讶的是，这些结果不能用预测的视觉表现来解释，因为模型预测不同的表达模式在不同的深度不会带来敏感性优势。这表明表达变化并没有赋予局部敏感性优势。因此，我们的发现与感官偏见假说的一个主要要求相矛盾。因此，需要测试其他解释种内基因表达变化的解释。
